Receiving circuit



Feb; 4, 1930. s, ANDERSON 1,745,347

RECEIVING GIRCUIYT Filed Aug. 29, 1923 3% h D W 3% W R Fatentecl Feb. 4, 1 930 1 UNITED sTATEs PATENT OFFICE SIDNEY" E. ANDERSOR'OF BROOKLYN, NEW'YORKfASSIGNOR TO WEsTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. 'A CORPORATION OF NEW YORK RECEIVING CIRCUIT Application filed August 29, 1923. Serial No. 659,885.

[The present invention relates to electric wave" reception and laii'i'plificat ion and more particularly to' plural stage radio frequency amplification H p 5 An Object of the invention'is to secure high amplification at radio frequencies in 'a'cir- "canpoesessin constancy and'stability of opcitation. V

. In a co pending application of Herald T.

"in 'Frii sfSerial N0. ciosl fii d May 28, 1923,

, afradio'receivingcircuit is' disclosed having a tuned' high frequency input circuit for a radio frequency amplifier,' in which the grid and filament of thehrst stageare connected 'l-5'across'a portion Of t'he inductance -of the t'unedcircuit' v'v'hi'le the plate is p'rovidedwith a connection through a small condenser to'a point (31f the'inductance onthe side of the filainenttap' opposite from the grid. lVhen this condenser has a "capacity of'the same rder of magnitude as the internal capacity Of the tube, it is found that an adjustment ma readily be obtained which Will render 1 the circuit stable as' rega'rds" any tendencyto developed sustained 'oscillations or singin' v %V here several stages ofradio frequency amplification 'are employed, there is found to'beatndency'for individual'stages to de- 30 'velop "Fsinging on" account of the resonant charactrist'ic's"of the radio frequency transformersor ether interstagecircuits the internal capacity of'the amplification tubes.

As is "Well knoiv'nfthis tendency to sing I limits'the amoiint of amplification 'vvhichcan be'obtained'in'any circuit so that the more effe'ctively'the 'Fsingin tendency can be re'dnced,-" .the greater 'can'be'theamplificatiorn' as well as the general stability and con- "40 etanc' efioperatio of'thei circuit. M

, Accordin'gto thei'nv'ention, each stage of a i plural stage amplifier circuit is balanced -againseidveiopin nee oseun ions 'or s ing 'byf'rnea'nsof a capacity external to the ,mbareriispposing the action Of'the internal capacity in "developing self sustaine'd 'oscillations. v v "Inthe drawings, Fig. 1 shovvs a typical radio receiving circuit embodying, in 'one for'mfthe anti-singing feature "O'f'the invention; and Fig. '2 is a similar representation of a modified form of receiver. v 7

Referring first to Fig. 1, an open antenna 1 is shoivn provided with the usual tuning elements andhaving its inductance associated in energy-transfer relation with the inductance 3 of the secondary tuned circuit 2Which comprises also the adjustable condenser 4. The first stage radio frequency amplifier A has its filament connected to an intermediate point 'of the inductance and its grid connected to a terminal of the inductance. Connection is madefroin the plate of this amplitier to' the second stage amplifier Ag through the radio frequency transformer T The plate oranode of the amplifier A also' is connected through the condenser 5to the termirial of the inductance 3 Opposite to that connected to the grid. The purpose of this connection Willbe described hereinafter.

The plate or anode of the amplifierA is connected by means of the radio frequency transformer T to the detector D and this anode alsois connected through the condenser 6 to the anode of amplifier Theoutput circuit of the detector D contains a receiver Ref suitabletype. The filaments of the tubes are supplied with heating current from source 7 and the anodes with space current from the" common source 8,

The circ uit of Fig.2 differs only slightly from that of Figll and a brief description of the points of difference ivill suflice. For the sake of illustration a loop antenna 10, tuned byvariable condenser 4, is shown connected to thefirst stage amplifier A in place of the openantenna of Fig. 1 although either type of antenna may be employed in connection with eitherfigure. In the modification shown inFig. 2,the condenser 6 corresponding to condenser 6 of Fig. 1, is connectedto thesame loop terminal as condenser 5.

In operation, the constants of the antenna land the tuned circuit 2, and the'coupling betWeent-hem orthe constants of the loop circuit if a loop is used, are adjustedto suit the Wave length and other conditions of any given case. The received radio frequency Waves impressed across the grid and filament of the amplifier A; ar amplified in this tube and transmitted through the radio frequency transformer T to the input side of the amplifier A where they are further amplified and transmitted through radio frequency transformer T to the detector. The detector operates in the usual manner to derive from the received waves the speech, music or other waves by which the radio wave is modulated at the transmitter.

On account of the unavoidable capacity which exists between the grid and plate elements of the vacuum tubes, there is a certain amount of energy directly transferred across the space between the grid and plate, these elements acting as a condenser. This capacity, therefore, afiords a coupling between the'grid and-plate circuitsand at the same time cooperatesfwith the inductance elements of thesecircuits to give the'circuits a natural period. Due to the amplifying action 'of'the tube, together with the tuning and feedback coupling afforded by the tube capacity, each tube acts or tends to act as a generator of oscillations provided the amplification factor is sufliciently large.

' As explained in Friis application, supra, the" condenser 5 also afiords a coupling between the plate and grid circuit'ofthe amplifier A and due to its connection to the opposite terminal of inductance "3 from that connected to the grid, the potential variations transmitted through the condenser 5 tothe grid'circuit are of such phase as to oppose the potential variations'transmitted back to the grid circuit through the grid-to-plate capacity. Condenser 5 therefore opposes the circuit. I p I GondensertS-of Fig. 1 or condenser 6 of Fig.

acts in a somewhat'similar manner to prevent the building up offsustained oscillations in the circuit of the-amplifier A or in the general amplifier circuit. J

"By reason of the fact that transformers are used to couple the amplifier tubes, a phase 7 shift is introduced between the stages. The

exact magnitude. of this phase shift depends upon the relative distribution of the various constants of the transformers. I

' It has been found in a radio frequency amplifier circuit employing transformers; for

coupling thetubes, that the amplifying factor has two maxima' occurring at two distinct frequency values. The" amplification maximum which occurs at the lower of the two frequencies appears to be due primarily to the parallel resonance of the inductance of thefsecondary winding with its effectivedistributed capacity and the efiective input capacity of the following tube. The amplification maximum occurring at the higher. frequency is due'primarily to the series resonance of the leakage inductance of the transformer with the same "capacity mentioned above- The relative phase of the plate and setting up of sustained oscillations in the tube In practice, it has been found that regardless of the direction of Winding of the transformers T and T a tendency of the circuit.

to sing at one of these two resonance points will be more effectively opposed by the circuit of Fig. 1 while with the same circuit arrangements the circuit of Fig. 2 will be more eflective to prevent singing at the other of the two resonance points. In some cases a combination of the arrangement of the balancing condensers as shown in Fig. 1 with the arrangement shown in Fig. 2 may be employed, for example, one of the two condenser arrangements may be used for certain stages andthe other arrangement for other stages. In general an arrangement of the balancing condensers and an adjustment of their magnitudes may readily be determined which will effectively oppose the'production of oscillations in all of the stages. On account of the lack of complete data as to the characteristics of radio frequency transformers it will ordi:

narily be impossibleto predict without an not to be construed as limiting the invention,

the scope of'which'is defined in the claims;

What is claimed is: 7

'1. In a receiving circuit a tuned inputcir-j cuit, a vacuum tube amplifier having fila-' ment, grid or impedance control and plate electrodes, the filament and grid being connected to different points of the inductance of said tuned circuit, a condenser of the order of magnitude of the inherent capacity b'etween said grid and plate connected between the plate electrodeand a point in the inductance on thegopposit'e side ofsaid'filament I connection fro nthe point to which the grid is connectechla se'cond' vacuum tube," a trans-. I

former having its primary winding 'connected between theplateand cathode offthe first tube and its secondary between theigrid and cathode, of the second tube, "and'a condenser connecting said two plates and having a;ca-'

pacity .of the orderof magnitude of the in-. herent capacity between the .grid and plate of said second tube. Y

2. In a wave repeating circuit, a plurality of vacuum tube repeaters connected in tandem, each tube having a cathode, an anode,

and a grid or control element, means including an adjustably tuned circuit for impressing on said repeating circuit the waves to be repeated, connections from the cathode and grid of the first tube to points on the inductance of said tuned circuit, a condenser connected between the anode of the first tube and a point on said inductance on the opposite side of the point of connection of the cathode from that to which the grid is connected, a transformer having its primary 

